The present invention relates to a device testing system used to detect and analyze a failure of a device that is being tested.
A device testing system used to detect and to analyze a failure of a DUT (Device Under Test: a general term for a device being tested), such as an LSI, conducts a test by converting a measured source current in the DUT into spectrum data and then analyzing the spectrum. According to this test, a predetermined test pattern is applied to the DUT, and the source current for the DUT obtained during the operation of the test pattern is converted into spectrum data. The thus obtained spectrum has a peak that is present only at integer times a basic frequency 1/T [Hz]; for example, when the period of time extending from the operational start of the test pattern to its end is defined as T seconds, the peak of the spectrum first appears at 1/T [Hz], and at 2/T [Hz], 3/T [Hz], . . . thereafter. Conventional art concerning such a device testing system is disclosed in, for example, the Unexamined Japanese Patent Application Publication No. Hei 9-211088.
While generally a device testing system can repetitively supply a test pattern, due to the effect produced by the structure of the measurement system, a source current having the same strength does not always flow across the DUT, even though the same test pattern is applied, and the strength of the source current more or less fluctuates. Especially when the DUT is a CMOS integrated circuit, substantially, no source current flows across the circuit when it is inactive, and the circuit is easily affected by slight current changes due to noise. Therefore, in a conventional device testing system that detects a failure by converting the source current of the DUT into spectrum data, there is a large variance in the measurement values.
When the source current of the DUT is converted into spectrum data, the spectrum generated is the result of the operating time required for one test pattern that is applied in the above described manner. Therefore, the precision of a failure detection process using the spectrum depends on the spectrum interval, which is consonant with the operating time for the test pattern. Thus, when the operating time is too short, a precise failure detection process can not be performed.
To resolve these shortcomings, it is one objective of the invention to provide a device testing system wherein variances in measurements can be reduced for the detection and the analyzation of failures experienced by DUTs, and wherein measurements using a fine source current spectrum are enabled in order to improve the rate of detection of DUT failures.
According to a first aspect of the invention, a device testing system comprises:
pattern supply means for supplying the same test pattern a plurality of times to a device being tested;
averaging means for measuring a source current for the device each time the test pattern is supplied, and for averaging the thus obtained values to provide an average source current measurement; and
detection means for detecting a failure of the device based on the average source current provided by the averaging means.
According to a second aspect of the invention, in the device testing system in aspect 1, the detection means converts the average source current into a spectrum, and employs the spectrum to detect the failure of the device being tested.
According to a third aspect of the invention, a device testing system comprises:
pattern supplying means for supplying to a device being tested a plurality of like patterns that are linked together;
measurement means for measuring a source current for the device when the linked test patterns are supplied; and
detection means for converting into a spectrum the source current measured by the measurement means, and for employing the spectrum to detect a failure in the device being tested.
According to a fourth aspect of the invention, in the device testing system in aspect 3 the pattern supplying means includes:
averaging means for supplying the linked test patterns to the device being tested, and for providing an average source current that is obtained by using the source currents that are measured by the measurement means when the test patterns are supplied. The detection means converts, into a spectrum, the average source current obtained by the averaging means, and employs the spectrum to detect a failure of the device being tested.
According to a fifth aspect of the invention, a device testing system, which is used to detect a failure of a device being tested, comprises:
a unit having a source current measurement function;
a unit for generating a test pattern and for controlling the test pattern;
a unit for converting, into spectral data, information for a source current for the device being tested; and
an averaging circuit for repetitively applying the same test pattern to the device being tested and for averaging the source current obtained for the device.
According to a sixth aspect of the invention, the device testing system in aspect 5 further comprises: a function for converting, into spectral data, data obtained by the averaging circuit.
According to a seventh aspect of the invention, when employing the device testing system in aspect 5 or 6, a plurality of the same test patterns can be linked together and applied to the device being tested in order to detect a failure.